Help w/ High power LEDs

Is there a good site or somewhere that a novice can get basic info on learning about/experimenting with high power LEDs? Recomended parts suppliers would be nice too! I'm interested in scratch building some light projects.
Thanks
AGUS

What type of LEDs are you looking at? The 5mm Superflux and the 10mm hi-outputs can readily be had from Hong Kong suppliers for very cheap. I'm working on a LED lighting project myself, and I'm using the 10mm ones.

I haven't played with those types myself, but from what I've been told by others "in the know" they do tend to be brighter than the standards, but they also generate a lot more heat, so you have to set them up with some form of heat sinking to keep the temperature down..

I'm working on a power LED lighting project too. The ones I've been looking at are Luxeon K2 emitters. Looks like the Q5 has a higher output, though. The K2's binned at the highest flux level put out around 130 lumens at 1.5 A, 113 lumens at 1 A--according to specs. The problem is that they don't have stock on those. The ones they do have stock on are only guaranteed to put out 30 lumens or so! The reps on the phone said that you can run them at the higher drive currents (1.5 A max), but the output will be inconsistent.

AGUS, what kind of questions did you have? I'm no expert, but I've been doing a lot of research lately so maybe I can help.

Well, basically, is there a difference between these and the standard round ones. Can I just use a resistor to drop the current below the max for the unit or must I use another way. I've seen what are called 'drivers' for these and don't know what they involve. Maybe they are no more difficult to use than the old type but I havn't been able to find any info at all. It looks like quite a few people are souping up flashlights with them. I know there is one company that sells LED landing lights for experimental aircraft but are wildly priced. That is sorta where I was headed. Thanks

Apart from the output, I don't know if there is practical or operational difference between power LEDs and standard one. I'm sure at the semiconductor level, they are probably pretty different, but that's over my head. From what I have learned, all LEDs are best powered by constant current sources. Current limiting resistors would be used if you were going to power the LED from a voltage source. I think the way that works is once the current going through the resistor reaches the limiting value, the voltage drop across the resistor is greater than the forward voltage of the LED, so no current above the limiting value can flow. A good reference I found is here (no product bias implied):

There's a formula in there for calculating the limiting resistor value that is product-independent.

As far as your question about drivers goes, these are basically power supplies that are designed specifically for powering LEDs. You'd want to make sure you had good prior knowledge of your load (LED array) in order to purchase the proper driver. There are plenty of them out there, so check out the options and specs to see what's available for your particular application.

I just used Luxeon K2 LEDs in a circuit for a project at school. I can tell you that they are very bright and have a quick response time. If you are using them you will want to use a constant current supply. I used a LM317 to proved the current and a high wattage resistor.
These LEDs drop about 2-3 volts. This is the circuit that was used in my project:

You can simply remove both transistors if you are simply connecting it directly to a supply. This was the setup used to turn the lights on at off using a micro controller (the HC11), the bottom transistor is wired to the MCU and the top transistor has the supply (12 volts) connected to it.

Hey transplant, what was the full part number of the K2's you used (i.e. which bin did they come from)? I'm trying to find some of the ones from the higher flux bins, but they don't seem to be available without a huge lead time. Also, if you could tell me where you got them, that would be great. Thanks!